1. Field of the Invention
The present invention relates to a driving control apparatus for a vibration wave motor (vibration type driving apparatus or motor).
2. Related Background Art
A known vibration wave motor (vibration type driving apparatus or motor) has the following characteristics. When the frequency of a driving voltage is decreased below a specific frequency, the rotational speed of the motor is abruptly decreased, and the motor is stopped.
In order to prevent this, a driving control apparatus for the vibration wave motor performs the following control operations: (a) a phase difference between an output signal from a so-called sensor-electrode and the driving voltage of the vibration wave motor is monitored so as to detect a vibration state of a vibrator of the vibration wave motor, and the frequency of the driving voltage of the vibration wave motor is controlled so as not to be that specific frequency in accordance with this phase difference; (b) the amplitude of an output signal from the sensor-electrode is detected, and the frequency of the driving voltage is controlled so as not to be the specific frequency or less in accordance with the detection result; and the like.
In addition, a high voltage is required to drive a vibration wave motor, (i) the driving voltage applied to the vibration wave motor must be boosted by a transformer, and the boosted voltage must be applied to the motor, (ii) a battery voltage must be boosted by a DC/DC converter or the like to a voltage required for driving the vibration wave motor, or (iii) a high-voltage battery must be used. A power supply unit in accordance with method (ii) is used in a conventional vibration wave motor driving control apparatus.
In the conventional driving control apparatus using a power supply unit according to method (ii), a large, expensive DC/DC converter is required to prevent an abrupt rotation stop phenomenon of the vibration wave motor. In addition, the capacity of a battery for applying an input voltage to the DC/DC converter must also be large. To prevent the rotation stop phenomenon of the vibration wave motor, the battery must be replaced with a new one long before the end of its service life, resulting in an economical disadvantage in efficient battery utilization. In addition, the running cost of a device incorporating a vibration wave motor is increased, and the weight and size of the device are undesirably increased.